Monday, January 26, 2009

Biodegradation of Polymers

I know, a pretty small topic, but getting bigger all the time. Over looking disolvable sutures which have existed for decades, and further overlooking the nasty marketing ploy of the "biodegradable" polymers that existed 20 years ago - a mixture of PE and corn starch, with only the carn starch being consumed and the PE being left as dust, large volume biodegradable polymers such as poly(lactic acid) are finally hitting the big time. Yes, you still need oxygen for these to degrade, so burying them in a landfill does nothing for the earth.

But on a smaller scale (and the point of this post), microbial degradation happens quite often on the surface of many plastics, and if the surface appearance is important such as with a work of art (free access), then even small amounts of degradation that wouldn't be a concern can become immensely important. Prior to reading this article, I knew that microbial life could live on the surface of plastics, but that it was because of the (consumable) dirt on the surface, not the plastic itself. While that is true, there are other options for life on clean surfaces. The plasticizers that are always migrating to surface of PVC become a food source once there, polyurethanes can be enzymatically degraded. Other examples exist, and in some cases where the polymer was applied as a "protective" coating to the work of art, it made the surface even more prone to attack. Again, not something that will help dispose of a pile of the polymer, but certainly something to be aware of in spots where the surface appearance is critical and duration matters.